1. Field of the Invention
The present invention relates to a reinforcing apparatus for bracing, splinting, or otherwise supporting vertical structures, such as utility poles, power distribution and transmission poles, telephone poles, and like poles and structures, against the forces exerted upon them by environmental factors such as transverse and shear winds. More specifically, the present invention is directed to an improved reinforcing apparatus which when secured to a utility pole and the like minimizes the tendency of the apparatus to twist and rotate under applied loads.
2. Description of the Related Art
Utility lines, such as those carrying electrical power, cable television signals or telephone signals, have traditionally been supported above ground using poles, and especially wooden poles. As used herein, the term "pole" includes various forms and definitions of elongated support members, e.g., posts and pilings, whether or not constructed of wood. Such poles must be capable of withstanding not only the columnar load applied by the weight of the objects supported thereon but also the transverse or horizontal load imposed by the transverse winds. In addition, after some years in service, wood utility poles tend to experience decay and rotting just below and slightly above ground level.
While the decayed region is normally relatively small and the penetration of the decay may be limited, the pole is nonetheless structurally weakened and may not be sufficiently strong to resist wind and other forces. Under these conditions, wind forces can result in a pole breaking and toppling, sometimes without warning.
Therefore, it is necessary to periodically replace older wooden poles. The demand for replacement poles, in combination with the demand for new poles, has become increasingly difficult to meet. Such a demand presents environmental concerns related to deforestation and the toxic effects of preservative chemicals used to treat the poles. In addition, replacement of existing poles is expensive and may require interruption of service to users of the utility. To overcome these and other problems associated with pole replacement, various methods and apparatus for reinforcing in-service poles have been developed to extend their useful life.
One technique for reinforcing utility poles is that of coupling an elongate brace or truss to the pole, in effect splinting or bridging across the weakened area of the pole. Such braces are customarily adapted to extend at least partway along the pole parallel to its longitudinal axis to provide support against transverse wind forces, and other loading conditions.
One such pole reinforcing apparatus is the Osmose.RTM. Osmo-C-Truss.TM. system. This reinforcing apparatus, developed by the inventor of the present invention, helps to restore the groundline strength of utility poles at a fraction of the cost of pole replacement. The Osmo-C-Truss.TM. comprises a C-shaped galvanized steel reinforcing apparatus which is secured to a pole by a plurality of galvanized steel bands fastened around the perimeter of the truss/pole assembly. The Osmo-C-Truss.TM. can extend the life of a pole for many years and is installed without interrupting power to utility customers.
In spite of the many advantages of the Osmo-C-Truss.TM., some performance issues are inherent in the use of a "C" or channel shaped reinforcing apparatus. One significant performance issue is related to the ability of a "C" or channel shaped design to withstand bending loads from a pole without twisting or rotating about the pole. One solution in the prior art is to increase or "beef up" the capacity of the apparatus by increasing its dimensions or the yield strength of the material of construction. However, these approaches fail to consider the underlying mechanical principles that govern the performance of such devices under load. Because the shear centers and the elastic axes of the reinforcing apparatus reside well outside the locus of the applied transverse load, there results significant torsional forces acting upon the reinforcing apparatus in addition to the expected bending forces. Specifically, the prior art has not taken into account the relationship between the location of the shear center of a pole reinforcing apparatus and the location of the transverse load applied to the reinforcing apparatus. The further the applied load is from the shear center and elastic axis, the greater the torsional forces that act upon the apparatus in addition to the bending forces. Torsional forces may cause the apparatus to shift its position about the circumference of the pole, i.e., rotate about the pole, to a disadvantageous position. Further, the reinforcing apparatus itself may twist and experience shape distortion when subjected to torsional forces, causing a reduction in performance; possibly less than the theoretical strength of the material of construction would afford.
Without a corresponding decrease in torsional rotation of the apparatus about the pole, or a reduction in the torsional forces themselves, the increased theoretical resistance to bending forces supplied by an apparatus having increased dimensions or higher yield material may be of little practical value. The reinforced apparatus may still undergo unacceptable rotation or twisting deformation causing premature failure before its theoretical bending capacity is reached. Further, while measures such as adding material of higher yield strength may increase theoretical bending support, they represent significant added costs, in many cases without yielding proportionate benefits or efficient results.
Accordingly, there has been a long-standing need for more efficient and cost-effective utility pole reinforcing apparatuses, and especially for a reinforcing apparatus that minimizes torsional forces and rotation of the apparatus about the pole, thereby increasing the ability of the apparatus to withstand transverse forces. This is especially important when using higher yield strength materials because to gain benefit from the higher material strength requires greater deflection of the pole from loading. Greater deflection of the pole causes more twisting and deformation of the reinforcing apparatus, which is likely to cause failure before the theoretical strength of the prior art reinforcing apparatus is met. The structures of the present reinforcing apparatus can withstand higher loading forces and, therefore, make better use of higher strength materials, such as high strength steels.